1. Field of the Invention
The present invention relates to an inkjet printing apparatus for ejecting ink onto a record medium to print, and also to an actuator controller and an actuator controlling method used in the inkjet printing apparatus.
2. Description of Related Art
A printing head in an inkjet printer includes therein an ink tank and pressure chambers. Each pressure chamber is supplied with ink from the ink tank. When an actuator is driven to change the volume of a pressure chamber, ink in the pressure chamber is pressurized to be ejected through a nozzle connected to the pressure chamber. Printing in a serial-type inkjet printer is performed with reciprocating such an inkjet printing head along the width of a print paper.
U.S. Pat. No. 6,527,354 discloses a technique for making a head in an inkjet printer eject two of large and small ink droplets through each nozzle successively in the order of the large and small ink droplets. In this technique, two different pulses, i.e., an ejection pulse and an additional pulse for pulling back part of an ink droplet, which is going to get away from the nozzle, into the ink passage, are applied in this order to the actuator unit. In case of a system for the so-called “fill before fire”, as the ejection pulse, a pulse is adopted having its pulse width substantially equal to half the acoustic resonance period of each pressure chamber.
In the above system, however, because two different pulses of the ejection and additional pulses are supplied to the actuator to eject two of large and small ink droplets successively in that order, the pulse waveform is relatively complicated. The more complicated the pulse waveform is, the more longer the occupation time of a series of the pulse train required for ejecting a sries of ink droplets. That makes difficult to achieve a high-speed printing. Moreover, at a certain printing speed, the following problem may arise. That is, the room is reduced for adding another pulses that improve the print quality by, e.g., canceling a pressure wave remaining within the ink passage after the first ink ejection operation when two ink ejection operations are successively performed.